1. Field of the Invention
This invention is directed to a device for determining proper oxygen lance height adjustment for a basic oxygen furnace (BOF) operation, and in particular, it is directed to laser based measuring apparatus capable of being positioned above the mouth of a BOF vessel so that repeated distance measurements to a target area within the vessel may be taken to provide a collection of measurement readings that are used to determine proper oxygen lance height adjustment for each or any selected heat manufactured during a steelmaking campaign. The laser-based measuring device includes an extendable optical head mounted within a protective air-cooled housing attached to an oxygen lance crane assembly, and a combined laser transmitter/receiver unit that communicates with the optical head from a remote position. The air-cooled housing is positioned above the mouth of a BOF at a location that provides the optical head with access to a line of sight extending down through the oxygen lance crane assembly, through a lance opening provided in the off-gas hood, and into the mouth of the BOF vessel. The laser-based measuring device further includes a spring loaded cylinder that is selectively operated to both remove a protective cover from an opening provided in the air-cooled housing, and extend the optical head outward from a stored position within the housing. The optical head is extended outward through the housing opening and into a line of sight down through the lance crane assembly, through the BOF mouth, and into the vessel interior. The spring loaded cylinder also selectively operated to retract the extended optical head back into its stored position within the housing and replace the protective cover over the housing opening. In its closed position, the protective cover shields the optical head and associated mechanisms from dust and fume generated during the BOF steelmaking process. Additionally, the air-cooled housing may also include a hinged or removable panel for convenience during maintenance and repair.
2. Brief Description of the Related Art
There has been a long felt need within the steelmaking industry to develop a more precise method for determining oxygen lance height adjustment. Correct lance height adjustment is critical to proper mixing at the steel/slag interface in a BOF steelmaking operation. In the past, such lance height adjustments were determined by calculations based on a once a day topographic measurement of the vessel interior. For example, a typical BOF heat cycle generally begins when an empty hot metal charging ladle arrives at the pouring station after the ladle has been used to charge a previous heat. A charge calculation is then made for the next scheduled heat and the ladle is filled with a calculated amount of molten iron. The charge calculation is generally made using a mass-energy balance model. The charge model calculates the weights of hot metal, cold pig iron, steel scrap, and flux materials that are used to produce a specified weight, temperature, and chemical analysis of steel at the end of the oxygen blow. In many BOF shops a predetermined weight of hot metal and scrap is weighed out early based upon the once a day topographical measurement of the vessel interior, and the final weights are obtained by trimming either the hot metal, the scrap, or both after the charge calculation for the heat has been completed. In the past, molten metal bath level was calculated using a once a day topographical or profile measurement of the vessel interior along with the charge model calculations. However, such calculations are inaccurate due to changing vessel shape. For example, after a finished heat is tapped, BOF vessels are rocked back and forth to provide a slag-splash coating that solidifies on the refractory lining to provide a protective coating against refractory erosion. Slag-splash coating is done before the remaining slag is poured from the vessel into a waiting slag car.
Slag splashing practice, in combination with the erosive effects of the hostile steelmaking process on the refractory lining, creates a dynamic, continuously changing interior space within the BOF vessel. As a result, bath level calculations of the past, based on a once-a-day vessel profile measurement, are inaccurate and may result in placing the oxygen lance either too high or too low with respect to the slag/metal interface. If an oxygen lance is positioned low, the velocity of the oxygen causes molten metal and slag to erupt from the vessel creating a hazardous condition. Low lance placement also causes skull to build up on the lance and causes overheating that reduces lance tip life. This condition also lowers the iron oxide content in the slag layer that floats on the surface of the molten metal bath. If a lance is positioned high, it becomes more difficult to lower the carbon level in the molten metal bath. A high lance will also generate higher oxygen levels in the cone portion of the furnace and a higher iron oxide content in the slag, both of which will cause excessive refractory wear.
Vessel measurements are taken only once a day because present state of the art vessel measuring devices and techniques require operators to take the vessel out of service so that the measuring apparatus, for example a laser device, can be moved into a measuring position in front of the BOF vessel. Such operations are time consuming and expensive with respect to productivity. For example, at the Bethlehem Steel Sparrows Point operation, it takes between about 45-50 minutes to produce a heat of steel, and each BOF vessel produces about 20 heats of steel per day. In a best case scenario, it takes operators about 20-30 minutes to take a vessel interior profile measurement. Therefore, from a lost-time viewpoint, such profile measurements are generally spaced apart as far as practical to avoid driving down steel production.
Various laser-based measuring devices are in use for detecting molten metal bath levels. For example, U.S. Pat. Nos. 5,190,717 and 5,090,603, issued to Bayliss, disclose a laser based metal pouring system for applying a molten metal coating to the surface of a steel substrate. The apparatus uses laser probes to measure coating thickness and to maintain a constant bath level in the pot. However, although Bayliss broadly teach using a laser beam to measure the level of a molten metal bath contained within a vessel, the drawing figures show an unprotected laser probe positioned above the molten metal bath. The Bayliss laser probe operates in an antiseptic environment as compared to the dust-laden, hostile environment above the mouth of a BOF converter. Therefore, Bayliss fails to recognize the problems associated with placing an electro/optical device within the hostile environment above a BOF steelmaking vessel, and his disclosure completely fails to provide any teaching or suggestion for overcoming such problems.
Another laser-based measuring device is shown in U.S. Pat. No. 4,899,994 granted to Zhidkov, et al. The 994 patent teaches mounting a xcex3 radiation transmitter and a xcex3 radiation receiver above the mouth of a BOF steelmaking vessel to measure the level of molten metal in the vessel. Such devices are very hazardous from a radiation viewpoint, and would likely not be used in the United States due to their high radiation levels. However, because such xcex3 radiation devices are likely not affected by high dust levels, the disclosure fails to address dust related problems associated with a BOF steelmaking operation. Accordingly, the inventors fail to teach, or even suggest, protecting their sensor from the hostile environment above a BOF vessel.
Therefore, there is a long felt need within the industry to provide a safe, radiation free, measuring device that will allow operators to make repeated vessel measurements in the hostile BOF steelmaking environment to determine critical O2 lance height adjustments with respect to the slag/metal interface without reducing productivity.
Accordingly, it is therefore a first object of the present invention to provide improved accuracy in oxygen lance height adjustment in a BOF steelmaking operation.
It is another object of the present invention to provide a measuring device capable of measuring distance to a target area within a steelmaking vessel without decreasing steelmaking productivity.
It is still another object of the present invention to provide a measuring device capable of measuring distance to a target area within a steelmaking vessel while the lance crane assembly associated with the steelmaking vessel is in a steelmaking position.
It is another object of this invention to provide a measuring device capable of measuring distance to a target area within a steelmaking vessel before the start of each heat produced during a steelmaking campaign.
It is still another object of the present invention to provide a measuring device capable of being located at a permanent operating position within the hostile environment above the mouth of a BOF steelmaking vessel.
Another object of this invention is to provide an improved method for determining lance height adjustment with respect to a calculated bath surface of a selected heat based upon a continuing series of measurement readings to a target area within a metallurgical vessel.
Other objects and advantages of the present invention will become apparent as a description thereof proceeds. In satisfaction of the foregoing objects and advantages, the present invention provides a measuring device adapted to measure a distance to a target area within a metallurgical refining vessel while an associated lance crane assembly is in its refining position above the metallurgical vessel. The measuring device includes an optical head that is positioned to direct to the target area an energy beam received from an energy source, and to direct to a processor an energy beam reflected from the target area. The optical head is contained within a housing and is attached to a movable mounting that may be selectively extended to expose the optical head to the target area, and selectively retracted to shield the optical head within the housing when measurements are not being taken.